ATR-SEIRAS Studies of Butadiene Electrocarboxylation in Aprotic Media

The electrocarboxylation of butadiene (BD) offers a sustainable route to hexenedioate synthesis through CO2 utilization. Hexenedioate can be converted into adipic acid, the main precursor to Nylon, which is currently produced from fossil-based feedstocks. However, key aspects of BD electrocarboxylation remain unclear, particularly the involvement of surface-bound intermediates and competing interfacial reactions, such as the CO2 reduction reaction (CO2RR). Herein, we employ in situ Attenuated Total Reflectance Surface Enhanced Infrared Absorption Spectroscopy (ATR-SEIRAS), electrolysis experiments with product analysis and density functional theory (DFT) to investigate BD electrocarboxylation on Au, Cu, and Pt. ATR-SEIRAS tracks the evolution of interfacial species and shows that BD suppresses the CO adsorption band on Cu but remains unchanged on Pt, consistent with DFT predictions that result from its preferential binding and the destabilization of BD chemisorption at increasingly cathodic potentials. Electrolysis experiments reveal higher hexenedioate Faradaic efficiency on Au, followed by Cu and Pt, while CO selectivity shows the opposite trend (Pt > Cu > Au), providing complementary evidence for metal-dependent trends observed in the spectroscopic measurements. Although CO still forms in the presence of BD, part of the CO2•- is consumed by BD to generate electrocarboxylation products, and the CO that is produced does not adsorb on Cu because BD or BD-derived species outcompete and displace it. These findings highlight the effect of BD adsorption and potential-dependent radical competition in shaping electrocarboxylation reactions, emphasizing the importance of considering interfacial contributions in the electrochemical process.